454 



JOURNAL OF ECONOMIC ENTOMOLOGY 



[Vol. S 



Sugar Cane Leaf-hopper Parasites 



The most noted case of introduction of beneficial insects in Hawaii 

 occurred in 1904-05, when Messrs. Koebele and Perkins introduced 

 from Australia and Fiji the egg-parasites for the sugar cane leaf-hop- 

 per, Perkinsiella saccharicida. These were three Mymarids {Parana- 

 grus optahilis, P. perforator and Anagrus frequens) and a Chalcid 

 {Ootetrastichus heatus) . Attempts were made to introduce others of the 

 many parasites that were found preying on leaf-hoppers in Australia 

 and Fiji, but these egg-parasites and a Dryinid were the only ones 

 that were successful. 



They soon became established and were spread throughout all the 

 sugar plantations, and within two years had made such a reduction 

 in the number of leaf-hoppers in the cane, that there was already an 

 appreciable amount of benefit derived, and after two more years there 

 was comparatively little complaint of injury or loss by the leaf -hop- 

 pers. Sugar cane was again grown without the severe setback which 

 young cane was always subject to when the leaf-hoppers were at their 

 worst, and which often resulted in ruining whole fields; in one instance 

 almost all the fields of a large plantation of 9,000 acres. 



The year preceding the establishment of the parasites, the esti- 

 mated loss from the leaf-hopper amounted to $3,000,000 for all the 

 plantations of the islands, and the sugar industry was threatened with 

 ruin. After the establishment of the parasites, this annual loss was 

 diminished yearly, until in a very few years the loss by leaf-hoppers 

 was considered negligible. Yet even now, after ten years, there are 

 occasional severe local outbreaks of the leaf-hopper, when whole fields 

 or spots in certain fields suffer considerably from their attack; but 

 this is usually only temporary, and there are no general outbreaks. 



Of the different parasites, one of the egg-parasites (Paranagrus 

 optahilis) has been the most useful one. The others are not always 

 to be found everywhere, but this one is always found aiwwhere and 

 everywhere that there are any leaf-hopper eggs for it to breed in. It 

 is usual to find 50 per cent or more of the eggs parasitized b}^ it. When 

 the shortness of its life-cycle is considered, it being three weeks as 

 compared with six weeks or more for the leaf-hopper, it is seen what 

 advantage it has in checking the latter. It has been the main factor 

 in this natural control of the leaf-hopper, though the other intro- 

 duced parasites and some local parasites and predators have been very 

 useful and played an important part. 



